The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Your Second Dose of Mounjaro — What to Expect
Your second dose of Mounjaro marks an important stage in tirzepatide treatment. Most UK patients receiving this GLP-1 and GIP receptor agonist on the NHS or privately will move from the initial 2.5 mg starting dose to 5 mg at week five. Understanding the timing, what to expect physically, and how your prescriber monitors your progress helps you manage the adjustment period effectively. This guide covers the second dose in NHS and UK private prescribing contexts.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
NHS Mounjaro Dosing Schedule and the Second Injection
The standard Mounjaro dose titration schedule in the UK follows NICE guidance and clinical trial protocols. Your second dose typically arrives at week five of treatment.
- Week 1–4: 2.5 mg starting dose (allows your body to adjust)
- Week 5–8: 5 mg second dose (standard escalation)
- Week 9–12: 7.5 mg if clinically appropriate
- Week 13+: Further escalation to 10 mg, 12.5 mg, or maximum 15 mg as needed
Each KwikPen contains four weekly injections. Your second dose is delivered in the same pen as weeks two, three, and four. Unlike some slimming injections, Mounjaro escalates quickly—the jump from 2.5 mg to 5 mg is substantial. NHS prescribers and private clinicians follow this schedule to allow adequate time at each dose level, monitoring how your body responds before further increases. If side effects are severe at 5 mg, your prescriber may delay escalation or adjust the plan.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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What Your Second Mounjaro Dose Means for Side Effects and Appetite
Many UK patients report that side effects from the 2.5 mg starting dose begin to settle by week five. However, the second dose—the 5 mg injection—often re-triggers mild nausea, changes in appetite, or stomach adjustments as your body adapts to a higher concentration of tirzepatide. This is normal and typically temporary.
Some patients notice stronger appetite suppression and earlier fullness signals with the 5 mg dose. Clinical trial data from SURMOUNT-1 shows meaningful weight loss acceleration happens at this dose level. Use our free GLP-1 weight loss calculator to project potential outcomes at 5 mg based on your current weight. Keep a progress tracker to log how you feel after your second injection—this information helps your prescriber decide whether escalation to 7.5 mg at week nine is appropriate for you.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
When exactly will I receive my second dose of Mounjaro on the NHS?
On the NHS, your second dose is administered at week five of treatment. If you received your first injection on a Monday, your second injection is due the following Monday, four weeks later. Private prescribers follow the same schedule. Your clinical team will confirm the exact appointment date. If you miss the four-week window, contact your prescriber—you can take the dose within a few days without restarting the schedule.
Is the second Mounjaro dose always 5 mg, or could mine be different?
The standard second dose is 5 mg according to NICE guidance and clinical protocols. However, if you experienced severe side effects at 2.5 mg, your prescriber may delay escalation or keep you at 2.5 mg for longer. This is a clinical decision based on your individual tolerance. Always discuss concerns with your GP or prescribing service before your second injection.
How is the second dose different from the first dose?
The second dose (5 mg) contains double the active tirzepatide compared to the starting dose (2.5 mg). This may increase appetite suppression and side effects like nausea or stomach changes. Most people tolerate it well after the adjustment period, and side effects often reduce after a few days. Your body's response to 5 mg helps determine whether faster escalation is suitable for you.
Can I compare Mounjaro vs Wegovy in terms of second-dose experience?
Wegovy (semaglutide) uses a different dose schedule—its second dose is 0.5 mg at week five, whereas Mounjaro's is 5 mg. Mounjaro escalates more rapidly overall. Both are GLP-1 (or in Mounjaro's case, GIP/GLP-1) medications, but individual response varies. Your prescriber will recommend the most suitable option based on your health profile.
Should I adjust my diet when I start my second Mounjaro dose?
No specific diet change is required when moving to your second dose. However, many patients find their appetite naturally suppresses more with 5 mg, so portion sizes may decrease naturally. Continue eating balanced, nutritious meals and staying hydrated. If nausea increases, eat small, frequent meals. Your prescriber can provide dietary guidance tailored to your individual response.
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